Difference in Effects of Gibberellins and Auxins on Wall Extensibility of Cucumber Hypocotyls
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Extensibility
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Extensibility
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Elongation
Plant Physiology
Cutting
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The role of endogenous gibberellin (GA) in the flowering of the short-day plant, Pharbitis nil, was investigated by using uniconazole, which is a specific inhibitor of GA biosynthesis. Both the endogenous GA level and flowering response decreased with increasing concentration of uniconazole applied via the roots. The strongest inhibition of flowering was observed when uniconazole was applied one day before a 15-h dark treatment. The inhibition by uniconazole was overcome by an application of GAs to the plumules, the order of effectiveness of the endogenous GAs in P. nil being GA1 ≧GA20>GA19≧GA44>GA53»GAH. This is the first report of the correlation between the endogenous GA level and flowering response in P. nil. It was found that endogenous GAs were required for the flowering of P. nil during or just after the dark period.
Pharbitis nil
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Abstract Ethylene or its precursor 1-aminocyclopropane-1-carboxylic acid (ACC) can stimulate hypocotyl elongation in light-grown Arabidopsis seedlings. A mutant, designated ACC-related long hypocotyl 1 (alh1), that displayed a long hypocotyl in the light in the absence of the hormone was characterized. Etiolatedalh1 seedlings overproduced ethylene and had an exaggerated apical hook and a thicker hypocotyl, although no difference in hypocotyl length was observed when compared with wild type.Alh1 plants were less sensitive to ethylene, as reflected by reduction of ACC-mediated inhibition of hypocotyl growth in the dark and delay in flowering and leaf senescence.Alh1 also had an altered response to auxin, whereas auxin levels in whole alh1 seedlings remained unaffected. In contrast to wild type, alh1 seedlings showed a limited hypocotyl elongation when treated with indole-3-acetic acid. Alh1 roots had a faster response to gravity. Furthermore, the hypocotyl elongation of alh1 and of ACC-treated wild type was reverted by auxin transport inhibitors. In addition, auxin up-regulated genes were ectopically expressed in hypocotyls upon ACC treatment, suggesting that the ethylene response is mediated by auxins. Together, these data indicate thatalh1 is altered in the cross talk between ethylene and auxins, probably at the level of auxin transport.
Etiolation
Elongation
Plant hormone
Wild type
Indole-3-acetic acid
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Arabidopsis hypocotyl cuttings were employed to study effects of auxin,ethylene and nitric oxide(NO) on adventitious rooting.The functions of auxin and ethylene signaling players cooperated with indole acetic acid(IAA) in adventitious rooting were also investigated.The results showed that treatment with either IAA or sodium nitroprusside(SNP,donor of NO) on Arabidopsis cuttings for 7 days could stimulate adventitious root formation,and the optimal concentration is 50 μmol·L-1 and 1 μmol·L-1,respectively;while ethylene played little role in rooting.Compared with wild type,sensitivity of auxin transportation and signal transduction and ethylene signaling-related mutants to stimulatory effect of IAA on rooting was reduced,especially gain-offunction of mutated IAA14(SLR).NO had synergistic role with IAA in adventitious rooting.
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A near isogenic line pair which differs only in the Uz and uz alleles was used for investigating the effect of uzu (uz) gene on the level of endogenous gibberellins in barley. Amounts of endogenous gibberellins in uzu plants were found to decrease in about a half to that of nami (normal) plants. Application of gibberellin A3 to uzu plants stimulated seedling growth and that of 2-chloroethyl trimethylammonium chloride, an inhibitor of gibberellin biosynthesis, to corresponding normal (nami) plants reduced both of stem length and endogenous gibberellin production.
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Carrington, C. M. S. and Esnard, J. 1988. The elongation response of watermelon hypocotyls to indole-3-acetic acid: a comparative study of excised segments and intact plants.—J. exp. Bot 39: 441–450. The auxin-growth response along the hypocotyl of Citrullus lanatus (Thumb.) Mansf. seedlings was studied. In excised segments, promotion of elongation was seen in all zones at the concentrations of IAA used (10–4–10–2 mol m-3). In intact plants, only the most basal zone showed unequivocal IAA-extension while in the most apical zone elongation was inhibited by auxin. This difference between segments and intact plants for apical zones suggests a modifying effect of the apex and cotyledons on the growth response. Indeed, removal of the apex and colyledons only affected elongation in the zones adjacent to the excision but only in buffer-treated plants, not auxin-treated plants. Auxin supplied apically to the intact plant only resulted in a short-lived promotion of elongation whereas basally supplied auxin gave a longer-lasting effect Zonal differences between auxin-promoted growth of excised segments suggests that sensitivity to auxin varies in the hypocotyl. The response of intact plants to auxin was shown to be more complex than in segments. Thus, responses given by segments are poor indicators of auxin activity in intact plants.
Elongation
Apex (geometry)
Indole-3-acetic acid
Apical dominance
Gibberellic acid
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Abstract The Arabidopsis hypocotyl, together with hormone mutants and chemical inhibitors, was used to study the role of auxin in cell elongation and its possible interactions with ethylene and gibberellin. When wild-type Arabidopsis seedlings were grown on media containing a range of auxin concentrations, hypocotyl growth was inhibited. However, when axr1-12 and 35S-iaaL(which have reduced auxin response and levels, respectively) were grown in the same conditions, auxin was able to promote hypocotyl growth. In contrast, auxin does not promote hypocotyl growth ofaxr3-1, which has phenotypes that suggest an enhanced auxin response. These results are consistent with the hypothesis that auxin levels in the wild-type hypocotyl are optimal for elongation and that additional auxin is inhibitory. When ethylene responses were reduced using either the ethylene-resistant mutantetr1 or aminoethoxyvinylglycine, an inhibitor of ethylene synthesis, auxin responses were unchanged, indicating that auxin does not inhibit hypocotyl elongation through ethylene. To test for interactions between auxin and gibberellin, auxin mutants were grown on media containing gibberellin and gibberellin mutants were grown on media containing auxin. The responses were found to be the same as wild-type Arabidopsis seedlings in all cases. In addition, 1 μm of the auxin transport inhibitor 1-naphthylphthalmic acid does not alter the response of wild-type seedlings to gibberellin. Double mutants were made between gibberellin and auxin mutants and the phenotypes of these appear additive. These results indicate that auxin and gibberellin are acting independently in hypocotyl elongation. Thus auxin, ethylene, and gibberellin each regulate hypocotyl elongation independently.
Elongation
Plant hormone
Wild type
Polar auxin transport
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SUMMARY Triiodobenzoic acid (TIBA) or morphactin (chlorfluorenol), applied to the base of the epicotyl of mung bean cuttings, inhibit root formation in the hypocotyl. Such inhibition occurs even when cuttings are supplied with auxin at the same time. Both treatments reduce the accumulation of radioactivity in the hypocotyl when [ 14 C]IAA is supplied to the primary leaves. Morphactin does not influence the uptake of [ 14 C]IAA supplied basally to cuttings, nor does it have any apparent influence on the distribution of radioactivity within the cutting. However, the extent to which [ 14 C]IAA moves from leaves to hypocotyl is influenced by the basal supply of auxin in which cuttings are placed. These observations are discussed in terms of the role of the leaves in auxin‐induced adventitious root formation.
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Cutting
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